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There are no 'official' definitions of the duration of spring, summer, autumn and winter for civil purposes. Many bodies, for example meteorologists, adopt a convention for the purpose of presenting statistics by grouping the twelve months of the year into four three-month seasons.

Different religions and cultures have their own conventions about the significance of the days of the week, and where in the week the cycle is said to begin. Even in modern times there are variations to accommodate specific needs.

Users of the MSF service receive predominantly a ‘ground wave’ signal. However, there is also a residual ‘sky wave’ which is reflected off the ionosphere and is much stronger at night, this can result in a total received signal that is either stronger or weaker.

The International Earth Rotation and Reference Systems Service (IERS), based at the Paris Observatory, announces twice yearly whether or not there will be a leap second at the end of the following June or December.

As UTC is running about one second per year faster than time based on the Earth's rotation (Greenwich Mean Time, or Universal Time), an extra second is occasionally inserted in the UTC time scale to let it fall behind and start catching up again.

The MSF radio signal has a very long wavelength (5 km) which is comparible or larger than dimensions of the metalwork of buildings and pylons which act as a screening mesh and greatly reduce the signal strength.

When they started in 1950 the MSF signals carried only seconds and minute markers, without any labels. In September 1974 a short burst of data at 100 bit/s was added during the first second of the minute to signal the hour and minute - the 'fast code'.

Miscellaneous FAQs

The time displayed on a well designed sundial will vary from the mean time during the year, up to 16 minutes ahead (November 3), and up to 14 minutes behind (February 11), only agreeing around April 15, June 13, September 1 and December 25th. Subject to these corrections a good sundial can be read to within a few minutes accuracy.

GPS has its own date and time scale for expressing satellite positions, based on counting weeks, and seconds within a week. To limit the size of the numbers used in the data and calculations the GPS Week Number is a ten-bit count in the range 0-1023, repeating every 1024 weeks.